A vertical column radiator would indeed be a good option, and I like the anthracite idea. Alternatively, if you could find a traditional tall victorian radiator (may not be easy to source) and finish it in a bronze/verdigris, it could work really well with your dark mint and would be a real statement! Your staircase is lovely, and I would go with a contemporary striped runner, white painted sides and a simple rod.

I always think that a hall with a seating area is just bliss for sitting down while pulling on your boots or flicking through a magazine or two! I would shelve the entire area that is before the post and have a built in seat with more storage above and below it to make life even more clutter free. Good luck hope it works out for you.

This space has so much potential, the architecture throughout is exceptional - it brings so many ideas to mind. I personally think that cooperating with some partition walls and bespoke installations will help towards achieving your goal. I am able to work with your existing drawings and improve on them, all done in AutoCAD to scale. Further down the line, I can create a 3D model for us to work with architecturally and interior design-wise. This will give you the advantage of seeing the space before investing in it - how the natural light reflects on the inside, how the materials appear, what shadows and reflections are created via the interior interventions. Please, drop me a message if you are interested. 😊

Not an area within my experience, unfortunately - not sure why there might be a big disparity in costs, but I would encourage you to get detailed quotes from the various possible suppliers and look cloesely to see the differences. There may be a variety of different ranges on offer, so you may not be comparing apples with apples. But in the window industry, it may also be folk just trying to get away with maximising profit wherever they can!